由下载地址得到下载包的精确大小

response = nil
Net::HTTP.start(‘some.www.server‘, 80) {|http|
  response = http.head(‘/index.html‘)
}
p response[‘content-type‘]

  def self.get_the_package_size origin_url
    if origin_url.present?
      if origin_url.index(".com")
        array = origin_url.split(".com").reverse
        url_end = array[0]
        url_begin = array[1].split("//")[1]
        url_begin = "#{url_begin}.com"
      elsif origin_url.index(".net")
        array = origin_url.split(".net").reverse
        url_end = array[0]
        url_begin = array[1].split("//")[1]
        url_begin = "#{url_begin}.net"
      else
        return ""
      end 
      response = nil 
      Net::HTTP.start(url_begin, 80, "10.103.11.54", 81) {|http|
        response = http.head(url_end)
      }   
      return response[‘Content-Length‘]
    end 
  end